Compressors and other machines use lubricants distributed by lubrication systems to reduce internal friction between parts by injecting the lubricant, such as oil or grease, into critical bearing surfaces and reciprocating parts junctions.
FIG. 1 shows a schematically typical lubrication system 100 for natural gas compressors 101. Such systems typically include a high pressure, low volume, positive displacement oil pump 102 including a lubricator gear box 104 that drives multiple lubricator pump roller rocker assemblies 106. Fluid is supplied to the system from a low pressure oil supply 108. Pressure valves 110, one for each roller rocker assembly 106 indicate the pressure at the pump outlets. The lubricant is pumped to divider blocks 120, each having multiple outlets 122 to distribute a desired amount of lubricant to lubricated equipment, such natural gas compressors 101, shown schematically without connections to divider blocks 120. The fluid pressure at the outlet of pump 102 is typically greater than about 500 psi, and the volume dispensed is typically less than about 10 or 15 gallons per day.
If a blockage occurs in the lubrication system, the positive displacement nature of the pump can cause a dramatic increase in the pressure in the lubrication system 100, which can cause components in the lubrication system to fail. Non-positive-displacement-pump lubrication systems, such as systems that use centrifugal or diaphragm pumps, are not as susceptible to damage from over pressure conditions. To prevent high pressure from damaging equipment in lubrication system 100, compressor lubrication systems typically include atmospheric rupture assemblies 132 as pressure relief devices. FIGS. 2 and 3 show a typical atmospheric rupture assembly 132. FIG. 2 shows that atmospheric rupture assembly 132 includes a metal disc 202 that prevents fluid flow under normal operating conditions but that ruptures when the pressure in the system 100 exceeds a certain value, venting the lubricant to atmosphere as shown in FIG. 3. If the flow of lubricant is interrupted, compressors and other industrial tools can be seriously damaged or destroyed. The rupture of the disk 202 of atmospheric rupture assembly 132 causes such an interruption of lubricant flow. To protect the equipment, a sensor on a “no-flow device” (not shown) is typically used to detect this loss of lubricant flow, and to trigger an alarm and eventual shutdown of the lubricated equipment.
Release of lubricant at very high pressures (up to about 7400 psi) to the atmosphere raises housekeeping, safety, and environmental concerns. After the initial rupture of the metal disc 202, lubricant is released onto the compressor frame and skid. The lubricant continues to flow until the compressor 130 is shut down by a lubricant no-flow device sensor device. The duration of continued flow varies from about a three minute interval for a digital no-flow device to about a twenty minute interval with an old style mechanical no-flow device. The resulting oil spill can be of significant size, is virtually impossible for the operator in the field to clean up, and raises environmental concerns.
Atmospheric rupture assemblies also raise safety concerns for workers in the area of the equipment. It is common for an operator to be near the compressor skid, monitoring pressure on a pressure gauge. The pressure gauge and lubricator pump are always in the same location as the atmospheric rupture assembly 132. The rupture of such assemblies has resulted in operators being struck by the high pressure lubricant and injured by pieces of the aluminum disc which blew out of the assembly when it ruptured.
Another problem with atmospheric rupture assemblies 132 is that they allow operators to insert more than one rupture disc 202. The installation of more than one rupture disc 202 in an assembly designed for a single rupture disc increases the pressure require to vent the system. Even with a blockage, the lubrication system may not be capable of achieving sufficient pressure to rupture multiple disks. This is a serious concern for the protection of the compressor components because the increased pressure may cause the divider block components and tubing to fail. If the excessive pressure is not relieved by the atmospheric rupture assembly, the compressor will continue to operate, potentially destroying the internal cylinder and rod packing components. The cost of replacement parts and lost production can be thousands of dollars.
Thus, while atmospheric rupture assemblies normally protect against high pressure damage, they have numerous shortcomings. Therefore, there is a need for a compressor protection assembly that reliably protects against excessive lubricant pressure without housekeeping, environmental, safety, and operating concerns.